Data usage even with data turned off

Somehow I have data usage (attributed to "System") even though I have data turned off. I had a 1MB Data Sense limit set, which was hit and the data usage stopped at 1MB. There is no way to set a Data Sense limit of zero. Maybe zero was thought to be unnecessary since you could turn off data...which would be true if it worked!

Maybe it happened during the 8.1 update process? Unfortunately I didn't check until now, so I don't know...I'll keep an eye on it.